According to this post, the probability of getting a 60g or 100g quest is approximately 19%. However, after 15 rolls-then-rerolls (so 30 rolls total), I have yet to see a single 60g or 100g quest. The probability of that happening by chance is less than 0.2%!

Am I doing something wrong? Do I need to do something to unlock 60g and/or 100g quests? Or have I just been getting insanely unlucky?

[Edit] I found theseposts claiming you need 50 wins to be eligible for the 60g and 100g quests. However, the wiki they credit no longer seems to say that. Was this just a rumor? Or was the behavior changed?

Note, relative to my other answer that this is strong evidence that there is unlock criteria for these quests due to the sample size being much larger and the experienced probability of encountering the 60/100 gold quests was 0. +1
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BlackVegetableMay 6 '14 at 15:03

1

I recently received the reward for winning 100 games in any mode. I have just shy of 25 total wins in play and arena mode. Yet i also receive only the quests you mention here over a lot (didn't count) of rerolls. The unlock criteria thus have to be either 50 wins in pvp or have something to do with the specific quests solved. I'm guessing the non-class ones are the relevant ones.
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sceniaMay 10 '14 at 15:19

Have you ever completed either one of the other 40g quests? The kill 40 minions or deal 100 damage one? And have you completed the 100 wins quest yet?
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sceniaMay 10 '14 at 23:11

@scenia: No, the only quests I've ever completed have been "<x> or <y> victories" and a single "3 victories". And no, I only have 27 wins.
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BlueRaja - Danny PflughoeftMay 11 '14 at 5:02

Not ever on that account? No practice mode or friend challenge wins to bring you up to 100? I just tried at 24, 25, 26 and 27 play wins sitting at 1 arena win, 100ish rerolls at each step, only getting beatdown, destroy them all, and 5 of the class quests. I recently solved 2 with paladin (which are not appearing) and i think i solved 3 victories a few days ago, not sure about the missing warrior quests. I start to think it's actually about solving each of the class quests... Your answers to my questions at the start of this comment might resolve the puzzle...
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sceniaMay 11 '14 at 6:36

EDIT: This answer is limited by the evidence in the Reddit post the OP originally linked to. More recent evidence suggests there are unlock requirements. Read on for a cautionary tale as to why you need larger sample sizes before jumping to conclusions though. :)

I agree with Studoku. However, two things are worth noting:

First, the exact chance of that occuring is just greater than 0.2% as the odds of not getting such quests 30 times is 0.813^30 = 0.002 (roughly; it is slightly higher.)

More importantly, the analysis posted had a sample size that isn't terribly large. Constructing a confidence interval for proportions in the range of [p - 1.96*sqrt(p*(1-p)/n), p + 1.96*sqrt(p*(1-p)/n)] gives us a 95% confidence interval from 11.38% to 26.02% . This means your odds of failure can only be assumed to be (1-0.1138)^30 = 2.67% with 95% confidence.

While this is lower than 5% (for the purposes of frequentist statistics) a Bayesian might suggest that a 2.67% chance of this happening is still more likely than both the odds of only your computer having a bug or Blizzard having secret unlock requirements that no one has figured out yet combined.

Either brand of statistician would probably suggest that the original sample size was far too small, and that more testing was needed.

Explanation:

The formula used to come up with the confidence interval is listed here. A confidence interval is a way of saying, I am X% certain that the true proportion (or mean) is between Y and Z. In this case (as is done commonly), I chose 95% for the confidence. This means, given our evidence, it is 95% likely that the true proportion lies between 11.38% and 26.02% according to that formula.

The probability of NOT getting an event is: 1 - p where p is the probability of the event occurring. The probability of NOT getting an event x times is (1 - p)^x. In this case, I chose the conservative side of the confidence interval as p, 11.38%.

Thus, I used (1 - 0.1138)^30 as the complement of this event happened 30 times. This equaled about 0.0267 which translates to 2.67% because probabilities are defined as being between 0 and 1.

Frequentist statistics are the classical (older) school of statistics that set a particular value (often called alpha) before an experiment such that if the probability of an event (or series of events) happening is lower than the chosen alpha, they will reject an old belief in favor of a new one. In this case, the old belief could be that the original poster was simply unlucky, and the new belief could be that there is some other mechanism at work which is influencing his/her quests. A common value for alpha is 0.05, or 5% probability.

Bayesian statistics is relatively newer and doesn't rely on strict alpha values for acceptance or rejection criteria. Instead, they consider a series of prior distributions, which basically means they consider more of the context of a situation to determine their judgments at the end of an experiment. Bayesian statistics is a bit trickier because calculating the prior distributions can often be difficult or time consuming. In this case, I didn't state the probability of just the poster's computer having a bug but I (lazily) assumed it was extremely low. For a humorous glimpse into these two fields of statistics, see XKCD.

Well, erm... You lost me at the third paragraph.
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peper757May 5 '14 at 21:59

Ah, sorry, I'll edit my answer with clarification when I get a chance.
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BlackVegetableMay 5 '14 at 22:06

While this answer is truly amazingly well written, i can't bring myself to voting it up because its conclusion is just wrong. There are definitely requirements and my current testing suggests they are connected to solving specific quests at least once.
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sceniaMay 10 '14 at 15:13

@scenia Right. The conclusion is based upon the evidence it had at the time of its writing. In that sense, the conclusion is mathematically sound. However, the newer evidence resulted in a more enlightened answer (which I upvoted). I'll edit this to clarify. While I don't think this is worthy of an upvote, I don't think it is worthy of a downvote at this point either.
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BlackVegetableMay 10 '14 at 15:39

I agree and did upvote after all. The edit makes it clear to what extent the answer is applicable, so my reason for not voting up is gone.
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sceniaMay 10 '14 at 15:44